1. Field of the Invention
The present invention relates generally to catheters. More particularly, the present invention relates to a non-metal reinforcing mandrel for use with such catheters.
2. Description of Related Art
In percutaneous transluminal coronary angioplasty (PTCA), catheters are inserted into the cardiovascular system via the femoral artery under local anesthesia. A pre-shaped guiding catheter is positioned in the coronary artery, and a dilatation catheter having a distensible balloon portion is advanced through the guiding catheter into the branches of the coronary artery until the balloon portion traverses or crosses a stenotic lesion. The balloon portion is then inflated with a fluid to compress the atherosclerosis in a direction generally perpendicular to the wall of the artery, thereby dilating the lumen of the artery. After the last dilation, the balloon is deflated so that the dilatation catheter can be removed from the dilated stenosis and blood flow can resume through the dilated artery.
Ongoing development work of the dilatation catheters has reduced the transverse dimensions of the catheters for angioplasty procedures both as to their outer diameters as well as to the wall thickness of the catheter's tubular components. This reduction has led to difficulties in designing dilatation catheters having small transverse dimensions while still maintaining adequate pushability for advancement of the dilatation catheter through the guiding catheter into the patient's coronary artery and across tight stenoses. The marginal or inadequate pushability has been particularly noticeable with over-the-wire catheters that have been adapted for use with guidewires having diameters not more than about 0.014 inch (0.356 mm).
One solution to this dilemma has been the use of a reinforcing mandrel 24, such as the one shown in FIGS. 1A and 1B. The catheter 10 typically has an inner tubular member 12 with an inner lumen 14 adapted to receive a guidewire with a maximum OD of less than about 0.014 inch. An outer tubular member 16 is generally disposed about the inner tubular member 12 such that the inner tubular member 12 extends through the outer tubular member 16 and an outer lumen 18 is defined therebetween. The inflatable member (e.g., a balloon) 20 has a proximal end 21 which is secured to the distal end of the outer tubular member 16 and a distal end 23 secured to the distal end of the inner tubular member 12 so as to seal off the outer lumen 18 and the interior of the inflatable member 20.
The reinforcing mandrel 24 is within the outer lumen 18 between the inner 12 and outer 16 tubular members and extends from the proximal end of the catheter 10 into the distal portion of the catheter 10 but typically ends short of the inflatable member 20. The mandrel 24 is usually a cylindrical, often tapered axle inserted onto a device such as a catheter 10 to provide support along the length of the given device. The mandrel 24 is typically secured at the proximal end of the mandrel 24 within the adapter (not shown) mounted at the proximal end of the catheter 10.
Although difficult to achieve during processing, it is often desirable to vary the diameter of the mandrel 24 to establish a predetermined amount of flexibility. For example, since it is generally desirable for the proximal section of the catheter 10 to be more stiff to assist in the catheter's pushability, the proximal section of the mandrel 24 is designed/fabricated to have a larger diameter than the diameter of the mandrel 24 in a more distal section of the catheter 10. The smaller diameter portion of the mandrel 24 extending into the distal section of the catheter shaft 10 preferably has a transverse dimension of at least 20% less than the transverse dimension of the proximal section of the mandrel 24. This variation in the diameter of the mandrel 24 provides flexibility in the distal portion of the catheter 10 and allows the catheter 10 to track over the guidewire while still maintaining excellent pushability.
The mandrel 24 of the prior art is fabricated from a metal or metal alloy (hereinafter metal) rod. The metal mandrels 24 known in the prior art, however, have several inherent limitations. First, metal rods are generally too stiff for angioplasty procedures, and a too stiff rod reduces a catheter's trackability over a guidewire or other medical device. Not only is the rod often too stiff, but a metal rod is also more difficult to process. For example, the metal rod must be ground to the desired diameter for the various (i.e., proximal and/or distal) section and often still retains sharp edges along its length that can damage the interior of the catheter shaft. Further, the dimensions of a metal mandrel are fixed during fabrication.
It would be advantageous to replace the metal mandrels of the prior art with a non-metal mandrel that has more easily varied dimensions and stiffness characteristics along the length of the mandrel. The ability to easily vary the dimensions and stiffness characteristics of a mandrel will also allow more freedom in the choice of materials for the catheter shaft itself. In other words, because the stiffness of the mandrel can be easily varied during processing, the proximal section of the mandrel can be made stiff enough to provide the desired pushability for the catheter. A mandrel having a stiff proximal section reduces the need for a stiff proximal section of the catheter shaft itself. Thus, the material for the proximal shaft of the catheter will no longer be limited to a stiff polymer. By allowing the use of a less stiff polymer in the proximal section, the non-metal mandrel will also substantially reduce the likelihood of kinking. In this manner, a mandrel having a stiffer proximal section will provide the desired pushability without having to sacrifice the flexibility of the distal shaft of the catheter.